F4 power amplifier

[R-K Rønningstad]

C3/R25 and C4/R24 are bootstrap networks for the front end.
They slightly improved the maximum output and bandwidth, but
their primary purpose is to protect the JFETs from over-voltage.

R24 and R25?
or ?

 

[Nelson Pass]

DC servo to null the output DC offset due to potentiometer drift, natural changes during the warmup phase, etc.

Depends on what you want. I get <10 mV after warmup.

 

[Nelson Pass]

R24 and R25?

Yes.....

 

[R-K Rønningstad]

Ahhh! I was looking at http://www.firstwatt.com/downloads/f4_om.pdf.
Could not believe you did not knew your own design .

rkr

 

[spencer]

Mr. Pass,

I do not have 220uF capacitor handy for C4 and C5 and I am now using a 330uF capacitor. Is that fine? Yes the drift of DC at out put is easily adjusted within 10mV. The drift is mainly on the bias of the mosfet when the amp warms up (from 0.3A till 0.5x A per fet).

Spencer

 

[Zen Mod]

..........

I do not have 220uF capacitor handy for C4 and C5 and I am now using a 330uF capacitor. Is that fine? Yes the drift of DC at out put is easily adjusted within 10mV. The drift is mainly on the bias of the mosfet when the amp warms up (from 0.3A till 0.5x A per fet).

Spencer

sometimes even your ( or mine- whatever) fancy schmancy 220uF elco have enough tolerance to approach 330uF in real life ;
accent is on "sometimes" , but that's the fact.
so- why worry........ at least not in that position ............
just use same specimens in sym. positions

 

[Kashmire]

OK ... thanks guys ... looks like a DC servo is overkill with the F4 topology. Great forum, thanks.

Also, R-K, thanks for answering the C3/R25 and C4/R24 question with a Pass original quote. I appreciate the clarification.

 

[Gyuri]

C3/R25 and C4/R24

Dear RKR!

Look at this:

http://www.passlabs.com/np/f4-power-amp.pdf

Regards:

Gyuri

 

[R-K Rønningstad]

Re: C3/R25 and C4/R24

Dear RKR!

Look at this:

http://www.passlabs.com/np/f4-power-amp.pdf

Regards:

Gyuri

Yes, that was the one I searched out, and made me understand it all.

RK

 

[Nicola]

If you had read the thread you would know that "some guy" from Lowther-America has compared them already. It is pointless to keep asking questions already answered in this thread - it is too long already!

Thank you for the comments, I had read the thread, especially this one (http://www.diyaudio.com/forums/showthread.php?postid=1260712#post1260712), i reckon is the one you refer to, but was hoping to get a bit more from a comparison between the F1 and the F4. Kind regards

 

[twitchie]

F1 vs F2 vs F3 vs F4

This is the post comparing the F1-F2-F3-F4 amps:

http://www.diyaudio.com/forums/showthread.php?postid=1152546#post1152546

Quote:

The F4 sounds like a cross between the F1 and the F3. Cleaner than the F2, a touch of sweetness, but the truth is still front and center. I have not heard this amp in my system (yet), so my thoughts about this may change. It is a very exciting product.

 

[Jon Ver Halen]

F1 vs F4 Bass

I use the F1 for basses (20hz - 630hz). I'm happy (very) with it only that in some instances in somehow lacks the power for the woofer. I'm considering changing for the F4. Since you have listened both amps, what are the main differences between both F1 & F4 listening wise ?

Hi Nicola:

An impossible question. Because the F1 is a current source, and the F4 is a voltage source, a bass system designed for the F1 would not work well with the F4, and one that works well with the F4 would not work will with the F1.

That being said, both have worked very well in bass note reproduction when used with an appropriate speaker. The F1, because of its lower power, would work best with hi-efficiency woofers. If you are having a power shortage, I would certainly consider using the F4 in bridged mode where you can get a up to 100 watts of power.

 

[spencer]

F4 going to finish and now under bias adjust.....

 

[spencer]

Bias total 1.5A per channel and take very long time to become stable. DC offset below 5mV for all channel. Supply voltege at +22/-22V by using two 18Vx2 250VA transformers.

 

[apassgear]

F4 going to finish and now under bias adjust.....

Good to see another F4 coming to life...very nice work Spencer


Those PCB are from PD?

Lets hear your first impressions of sound

 

[Nicola]

Re: F1 vs F4 Bass

This is the post comparing the F1-F2-F3-F4 amps:

http://www.diyaudio.com/forums/showthread.php?postid=1152546#post1152546

Hi Nicola:

An impossible question. Because the F1 is a current source, and the F4 is a voltage source, a bass system designed for the F1 would not work well with the F4, and one that works well with the F4 would not work will with the F1.

That being said, both have worked very well in bass note reproduction when used with an appropriate speaker. The F1, because of its lower power, would work best with hi-efficiency woofers. If you are having a power shortage, I would certainly consider using the F4 in bridged mode where you can get a up to 100 watts of power.

Many thanks for the comment. This is exactly what i'm trying to find out. The woofers are around 99db, but if I compare the F1 with a classical voltage 20 or 40w class A amps, with some instruments it seems to lack the headroom, like there is a more limited power available especially with chords / piano / cello - where the instrument is fast in its attack. But on the other side none of the voltage amps have this control... so as you wrote it is like strawberry or vanila... Kind regards

Specs from woofer are
SPL: 99dB enclosed in box reaches 105db 1m / 1w +- 2bd
Fc: 43 Hz (Qes: 0,34, Qts: 0,33, Qms: 10,5, VAS: 231, Re: 4,8 Ohm ,EPB: 126,5)

 

[vizion]

Can the F4 be driven with 2.8vrms from a source unit ?

 

[Dougie085]

yeah I was wondering something of the same sort will a preamp with an 18.5 db gain be enough for the F4?

 

[mpmarino]

 

[Magura]

If you don't answer the boys....you can't have any cookies


Magura